TSH-secreting pituitary adenoma — SCE Endocrinology MCQ

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HardPituitaryTSH-secreting pituitary adenomaSCE Endocrinology

A 49-year-old man has repeated TSH 5.8 mU/L with free T4 22 pmol/L and free T3 6.8 pmol/L. He is clinically mildly thyrotoxic. Alpha-subunit is raised and pituitary MRI shows a 12 mm lesion. What is the most likely diagnosis?

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Correct answer: A — TSH-secreting pituitary adenoma

TSH-secreting pituitary adenoma is best because inappropriately raised TSH with high thyroid hormones, raised alpha-subunit and pituitary macroadenoma supports TSHoma. The alternatives are less appropriate because primary hypothyroidism has low free T4; Graves' suppresses TSH; resistance usually has family history and normal alpha-subunit; biotin interference should be excluded but does not explain the MRI finding. The SCE teaching point is to integrate the clinical pattern, biochemistry and context rather than treating an isolated result.

Reference: European Thyroid Association central hyperthyroidism guidance